(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a multi-segment alignment mark that can be used for a variety of lithography masking processes in the fabrication of integrated circuits.
(2) Description of the Prior Art
In the fabrication of integrated circuit devices, multiple layers of conductors and insulators are deposited and patterned to construct the integrated circuit. It is critical to align each subsequent layer with the previous layer with precision. This is typically accomplished by using alignment marks. A wafer stepper tool uses the alignment marks on a wafer as a reference point for adjusting a reticle over the wafer. The reticle contains the pattern to be generated within the layer. The reticle must be precisely aligned to the previous layer. A wafer stepper uses one of at least three methods to detect the alignment marks; these are light interference, bright field contrast, or dark field polarization effect.
For example, wafer alignment on an ASML stepper uses zero marks. For oxide chemical mechanical polishing (CMP) processes, zero marks are distorted at the metal layers due to oxide residue left on the marks. Target repairs at via layers are necessary to ensure that the zero marks are completely clean and can continue to be used. ASML's scribeline primary marks (SPM) have been developed to replace zero marks. The segmentation of the SPM marks determines signal strength and so is an important criteria for good alignment. For a foundry using this alignment scheme, different segmentations must be tested to find an optimized segmentation for each of the different processes. This testing requires laborious effort.
U.S. Pat. No. 5,627,624 to Yim et al shows a test reticle and alignment mark optimization method. U.S. Pat. No. 5,496,777 to Moriyama teaches forming alignment marks in enlarged portions of scribe lines. U.S. Pat. No. 5,401,691 to Caldwell discloses an inverse open frame alignment mark. U.S. Pat. No. 5,369,050 to Kawai discloses an alignment mark having a groove around it. U.S. Pat. No. 5,648,854 to McCoy et al discloses an alignment system using global alignment marks.